Pressure-Induced Polymorphic Transformations of Ethylenediamine Bisborane
Rongfeng Guan, Pan Wang, Yang Song, Viktor N. Staroverov
Abstract
Pressure-induced phase transitions of crystalline ethylenediamine bisborane (EDAB), a prospective hydrogen storage material, are investigated using vibrational spectroscopy, X-ray diffraction, evolutionary crystal structure prediction, and density functional theory. The results indicate that EDAB undergoes two transitions in the 0–17 GPa pressure range: the first one is near 1 GPa, from the orthorhombic ambient-pressure Pbca structure (phase I) to a monoclinic structure of P21/c symmetry (phase II); the second is near 7 GPa, from phase II to another P21/c structure (phase III). The latter coexists with phase II and remains the most stable form of EDAB up to at least 15 GPa. Unlike phase I, phases II and III have multiple dihydrogen bonds between neighboring EDAB molecules. The findings provide information for evaluating EDAB as a candidate material for hydrogen storage.